Best practice for defining values tor modules (vars vs locals)

Terraform
1

Hi, I wanted to get some feedback on 2 possible ways to define variables for a module.
Hopefully the description is clear.

Case 1 seems cleaner, or at least more properly defined? However, every module variable needs to be defined twice (in main and in module).

Case 2 has less definitions, and feels less bloated. I want to avoid though definitions that are hacky or not clean.

Same between both Cases

Module_A.variables.tf (var a1, var a2)
Module_B.variables.tf (var b1)

Case 1

main variables.tf (var a1, var a2, var b1).
main terraformv.tfars (a1=…, a2=…)
main.tf - Module_A.a1=var.a1. etc

Case 2

main variables.tf (locals{ a1=…, a2=…, b1=…}
main.tf - Module_A.a1=local.a1. etc

I’m very new to TF, so I’m open to hear different opinions, or downsides to either implementation.

Thanks!

2

Use locals when the target audience for customizing the values is people working on the Terraform configuration code in a text editor.

Use variables when the target audience for customizing the values is a source outside of the Terraform itself - for example, if you want to use the same Terraform configuration code in multiple different Terraform Cloud workspaces, with different variable values.

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